The system, which is available on the Volvo XC60, works by monitoring traffic in front of the vehicle. When driving at a speed of between two and 19 miles per hour, the car can apply the brakes should forward traffic suddenly do the same. When the difference in speed between your car and one in front of you is nine mph or less, the Volvo will brake quickly enough to avoid an accident. Above that threshold and you're most likely going into the car in front of you but the damage will be greatly reduced compared to an accident involving cars not utilizing the City Safety System.